Electroplating rack



Aug. 4, 1959 R. o. HENSON 2,398,285

ELECTROPLATING RACK Fil ed Feb. s, 1958 46 INVENTOR flu @Zwsm x ATTRNEY United States Patent 2,898,285 ELECTROPLATING RACK Roy 0. Henson, Flint, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application February 3, 1958, Serial No. 712,910 I 4 Claims. (Cl. 204-297) support rack generally consists of a metal frame member having a coating of nonconductive and chemically inert material, such coating being necessary to prevent the deposit of plating metal on the rack thus allowing cost savings, longer rack life, and an improved deposit on the workpieces.

One of the characteristics of such an electrolytic process is the tendency of the plating deposits to feather or burn along any sharp edges or points on the parts being plated. This condition is caused by the strong electrical current flow between such edges or points and the anode. To reduce the current fiow in these areas, robbers are placed on the plating racks opposite or adjacent such edges or points on the workpieces. These robbers consist of conductors which are electrically connected to the rack and which, therefore, also serve as the cathode. The conventional means for providing these robbers is to merely strip away a portion of the insulating coating on the rack at the desired locations so that the exposed metal will divert the current away from the parts being plated. A problem that arises from this practice is the accumulation of plating material on the racks at the robbers, this metal build-up being commonly referred to as trees. Because of such accumulation it is necessary to frequently remove the racks from service and remove the 'trees by time-consuming grinding or chiselling operations. In addition, the insulating material on the rack adjacent the robbers is very often cut or torn during the grinding or chiselling operations, thus resulting in reduced rack life.

It is an object of the present invention to solve the aforementioned difliculties by the provision of an improved plating rack having longer life and requiring less maintenance to remove metal deposits.

Another object of the invention is the provision of an electroplating fixture having an improved robber which results in cost savings and which requires less maintenance work.

These objects are carried out in accordance. with the invention by forming the robber of a conductive material which is electrically connected to the cathode circuit and which is easily stripped or peeled from the base on which it is supported. After there is an accumulation of metal on the robber such as requires removal, the robber is merely stripped away from the rack or other supporting base and a new robber applied therebydispensing with time-consuming and costly grinding and chiselling operations.

Other objects and advantages of the invention will appear more clearly from the followingdescription of a preferred embodiment and from the accompanying drawings in which: i

Figure 1 is a side view in partial'section of a plating apparatus embodying the present invention;

, ice

Figure 2 is a top view of one of the robber bars shown in Fig. 1; 5

Figure 3 is an enlarged view of one of the robbers shown in Figures 1 and 2;

Figure 4 is a view taken on the line 44 of Figure 3; Figure 5 is a view taken on the line 5-5 of Figurej 3; Figure 6 is a view similar to that shown in Figure 4,

but illustrating a different means of establishing electrical contact with the robber; and

Figure 7 is an enlarged sectional view of the contact finger portion of the plating apparatus shown in Figure'l.

Referring now to Figure 1, there is shown for purposes" of illustrating the invention, a platingapparatus for copper plating steel parts and includinga tank 10 containing a plating electrolyte 12 and a workpiece support fixture 14. In some instances the tank 10 may be made of metal and serve as the anode; however, in the embodiment shown the tank is constructed of a nonconductive material chemically resistant to the electrolyte 12 and the anode (not shown) may be any suitable conductor suspended into the electrolyte. It is to be understood, of course,

that the invention may be used in baths for plating metalsother than copper, such for example, as nickel, chromium, zinc, etc.

The fixture 14 comprises a hanger 16 'from which is suspended a rack 18. This rack, which may be made of metal and coated with an organic plastic or other inert material resistant to chemical attack by electrolyte 12, is provided with fingers 20 and with other suitable means such as are indicated at 22 and 24 for holding a work piece 26 in proper position within the tank; In the particular apparatus shown, the flanged or cupped ends of the workpieces, which are automobile. bumpers, are filing on fingers 20, the bumpers being maintained aligned by contact with members 22 and 24. The inert coating of the rack may, for example, be a vinyl plastisol as conventionally used for this purpose, and a typical composition of which is 55% polyvinyl chloride, 35% plasticizer and the remainder filler and stabilizer. Electrical current is supplied through the rack 18 and may be conducted to the workpiece 26 through the end of finger 20 to allow the workpiece to serve as the cathode. Other workpieces 28 and 30 may, of course, be supported within the electrolyte in the same manner as described above with relation to the workpiece 26;

Since the end portions of the particular workpiece shown present relatively sharp edges 32 and 34, robber bars 36 and 38, which are electrically connectedto the cathode circuit and which may be secured to the rack 18' to form a part thereof, are provided in these areas. As

, can best be seen in Figure 2, each of these robber'bars includes a metal member 40 which may be welded or i bar and which is electrically connected to the metal member 40. In order to better assure adherence of the layer 46 to the bar until it is desired that'itbe removed, itf'is preferable to continue the layer at least in some area's,

, around the bar tothe side oppositely disposed from the workpiece. Such a continuation of the layer 46 is shown,

for example, at 47.

The preferred means for establishing electrical contact between metal member 40 and the conductive layer 46 is shown in Figure 4 and comprises a weld-metal projec -i tion 48'which extends through the coating Maud-coin Patented Aug. 4, 1 9 59 through-the coating 44in one area, as shown at 50, to

contact the metal member.

" Anysuitable-material may beused for the layer 46,

the requirements being that the material be easily remov-.

able from the coating 44, that it be electrically conductive, and that it be chemically inert with respect tothe bath in which it is used. In the preferred embodiment the layer 46 comprises a mixture of fine powdered metal, such as copper or bronze, and an organic polymeric material. For example; a suitable composition for layer 46 is: 50% copper powder and the remainder, cellulose nitrate lacquer or polyethylene as a binder. The vinyl plastisols which are rubber-like materials conventionally used to coat electroplating racks and which consist, in general, of plasticized polyvinyl chloride are preferred as the binder. for the metal powder. Thus, a very suitable composition for forming the layer 46 consists of a mixture of 50 parts by weight super-fine copper powder and 250 cc. of a solution containing one part by weight vinyl plastisol and two parts by weight solvent. A typical vinyl plastisol composition which may be used in the aforesaid mixture is: 55% polyvinyl chloride, 35% dioctyl phthalate or tricresylphosphate plasticizer, 8% of a filler such as whiting, and 2% dibasic lead phosphate as a stabilizer. Any suitable solvent for the plastisol maybe used in the mixture, for example, acetone, methyl ethyl ketone, methyl isobutyl ketone or the like. The mixture is applied to the robber" bar by a painting or other suitable coating operation after which the solvent evaporates leaving a thin con-.

ductive layer of the copper powder-plastisol binder mixture, i.e., 50 parts by weight copper powder and approximately 80 parts by weight binder. This composition is particularly suitable as the conductive layer 46 where the coating 44 consists of a vinyl plastisol.

It is to be understood, of course, that the selection of the conductive layer material will depend largely on the compositon of the coating 44, in all instances it being required that the layer be relatively easily removable by stripping or peeling and not require grinding or similar time-consuming operations.

In operation, the invention works as follows: With the electroplating apparatus and workpieces assembled as shown in Figure 1 and as described above, electric current is passed between the anode and the workpiece, which serves as the cathode, for a sufiicient period of time to deposit a plate of the desired thickness. During this deposition the robbers comprising the conductive layer 46, prevent feathering and burning at the edges 32, 34 of the workpieces. 'After a number of such plating operations the robbers 46 will have acquired a considerable accumulation of plating metal as shown at 52 in Figures 4 and 5, at which time a worker can easily and quickly peel or strip off the layer 46 and provide a new such conductive layer by a painting or other suitable coating operation as described previously. With such new coating 46 the apparatus is again ready for further use. Also, the plating metal which has accumulated on the stripped robbers may be easily salvaged by merely removing the conductive layer therefrom.

While the conductive coating as shown at 46 has been described with specific reference to its use as a robber it will be understood that such a coating also has utility as an electrical contact between the workpiece and the rack. Thus, rather than peel off the plastic rack coating at the end of finger 20 to form a contact, it is highly advantageous to coat the plastic at the end of the finger with a layer of conductive material which is electrically connected to the metal frame of the rack. This is shown in Figure 7 wherein 54 is the metal base member of finger 20, 56 is the nonconductive coating and 58 is a conductive layer of metal powder plus binder. Electrical contact between layer 58 and metal base member 54 is established at 60 through an opening provided in coating 56. The same material can be used for layer 58 as for' the robbers as heretofore described. In this manner, the accumulations of plating metal wihch gather at the contacts can be easily removed by stripping the conductive layer from the plastic coating as described above.

It is to beunderstood that, although the invention hasbeen described with specific reference to a particular em-' bodiment thereof, it is not to be so limited since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

What is claimed is: Y

1. An electroplating bath fixture comprising a support for the workpiece to be electroplated and a robber bar connected to said support and positioned adjacent the normal position for the workpiece, said robber bar including a metal member having a coating of organic polymeric,

' nonconducting material thereon, a layer of conducting material on said nonconducting coating, said layer comprising a mixture of metal powder and a binder of or-v ganic polymeric material, and means extending through said nonconducting coating establishing electrical contact between said metal member and said conducting layer.

2. An electroplating bath fixture comprising a support for the workpiece to be electroplated and a robber bar connected to said support and positioned adjacent the normal position for the workpiece, said robber bar in-. cluding a metal member having a coating of nonconducting organic polymeric material thereon, a layer of conducting material on said nonconducting coating, said layer comprising a mixture of metal powder and an or-- ganic polymeric binder adhering to said nonconducting coating but removable therefrom by stripping, and means establishing electrical contact between said metal member and said conducting layer, said means comprising a metal projection on said member extending through said non conducting coating and contacting said layer.

3. A workpiece support rack for use in an electroplat: ing bath comprising a metal frame, a metal finger to support the workpiece secured to said frame, a nonconduct ing coating on siad frame and said finger and means for. establishing electrical contact between said finger and a workpiece supported thereby, said means comprising a layer of a mixture of metal powder and an organic polymeric binder on the coating on said finger in electrical contact with said finger and positioned to contact the workpiece.

4. In a workpiece support rack for use in an electro: plating bath, a metal frame having an organic polymeric coating thereon, means for establishing electrical contact between said frame and a workpiece supported by said rack, and a robber positioned to be adjacent said workpiece, said robber comprising a metal member having a layer of nonconducting organic polymeric material thereon, a conducting layer of a mixture of copper powder and organic polymeric binder adhering to said layer of nonconducting material but removable therefrom by stripping and means extending through said nonconduct.

nical Society, vol. 19 (1943 -1944), pages 37, 38, and

ing material for establishing electrical contact between said metal member and said conducting layer.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Leadbea'ter: Journal of the Electrodepositors Tech-' Fig. 3 (opposite page 42). 

1. AN ELECTROPLATING BATH FIXTURE COMPRISING A SUPPORT FOR THE WORKPIECE TO BE ELECTROPLATED AND A ROBBER BAR CONNECTED TO SAID SUPPORT AND POSITIONED ADJACENT THE NORMAL POSITION FOR THE WORKPIECE, SAID ROBBER BAR INCLUDING A METAL MEMBER HAVING A COATING OF ORGANIC POLYMERIC NONCONDUCTING MATERIAL THEREON, A LAYER OF CONDUCTING MATERIAL ON SAID NONCONDUCTING COATING, SAID LAYER COMPRISING A MIXTURE OF METAL POWDER AND A BINDER OF ORGANIC POLYMERIC MATERIAL, AND MEANS EXTENDING THROUGH SAID NONCONDUCTING COATING ESTABLISHING ELECTRICAL CONTACT BETWEEN SAID METAL MEMBER AND SAID CONDUCTING LAYER. 